Divided internal combustion chamber engines having a main combustion chamber and an auxiliary combustion chamber are well known. In such engines, communication is provided at selected times between the main combustion chamber and the auxiliary combustion chamber in order to firstly inject compressed air from the main combustion chamber (during the compression stroke) into the auxiliary chamber, and then at approximately top dead centre, after ignition of fuel and the compressed air within the auxiliary chamber, allowing combustion products to flow from the auxiliary chamber into the main chamber.
This control of fluid communication has been effected by the use of a valve known as a “flow modulator”. Typically the valve terminates the injection of compressed air from the main combustion chamber into the auxiliary chamber at about 25° before top dead centre. By terminating the flow of compressed air a this time, the compression ratio in the auxiliary chamber is limited to around 9:1, which is considered ideal for spark ignition. A dedicated fuel injector is provided to inject a small volume of fuel into the auxiliary chamber to be mixed with the compressed air within the auxiliary chamber in an amount to provide a slightly rich mixture
At top dead centre the compression within the main chamber would reach a pressure in excess of 300 psi. However a spark plug in communication with the auxiliary chamber is timed to produce a spark shortly after 25° before top dead centre so that the air and fuel within the auxiliary chamber has been combusting for slightly less than the time required for the engine to turn from 25° before top dead centre to top dead centre. As a result the pressure within the auxiliary chamber is substantially above the pressure within the main combustion chamber.
At top dead centre, the valve opens so that the combustion products within the auxiliary chamber are energetically ejected into the main combustion chamber to initiate combustion of the fuel/air mixture therewith.
It is an object of the present invention to provide an alternate form of an internal combustion engine with a divided combustion chamber.